diff --git a/e2e/tests/sync/supersync-account-deletion.spec.ts b/e2e/tests/sync/supersync-account-deletion.spec.ts
new file mode 100644
index 0000000000..551692e65a
--- /dev/null
+++ b/e2e/tests/sync/supersync-account-deletion.spec.ts
@@ -0,0 +1,190 @@
+import { test as base, expect } from '@playwright/test';
+import {
+  createTestUser,
+  getSuperSyncConfig,
+  createSimulatedClient,
+  closeClient,
+  deleteTestUser,
+  waitForTask,
+  isServerHealthy,
+  type SimulatedE2EClient,
+} from '../../utils/supersync-helpers';
+
+/**
+ * SuperSync Account Deletion E2E Tests
+ *
+ * These tests verify client behavior when:
+ * - User account is deleted on the server
+ * - Client tries to sync after account deletion
+ *
+ * Prerequisites:
+ * - super-sync-server running on localhost:1901 with TEST_MODE=true
+ * - Frontend running on localhost:4242
+ *
+ * Run with: npm run e2e:supersync:file e2e/tests/sync/supersync-account-deletion.spec.ts
+ */
+
+const generateTestRunId = (workerIndex: number): string => {
+  return `${Date.now()}-${workerIndex}`;
+};
+
+base.describe('@supersync SuperSync Account Deletion', () => {
+  let serverHealthy: boolean | null = null;
+
+  base.beforeEach(async ({}, testInfo) => {
+    if (serverHealthy === null) {
+      serverHealthy = await isServerHealthy();
+      if (!serverHealthy) {
+        console.warn(
+          'SuperSync server not healthy at http://localhost:1901 - skipping tests',
+        );
+      }
+    }
+    testInfo.skip(!serverHealthy, 'SuperSync server not running');
+  });
+
+  /**
+   * Scenario: Client detects auth error after account deletion
+   *
+   * Tests that when a user's account is deleted on the server,
+   * the client shows an appropriate error indicator.
+   *
+   * Actions:
+   * 1. Create user and client, sync successfully
+   * 2. Delete user account on server
+   * 3. Client tries to sync again
+   * 4. Verify client shows error (snackbar or error icon)
+   */
+  base(
+    'Client shows error after account deletion',
+    async ({ browser, baseURL }, testInfo) => {
+      testInfo.setTimeout(90000);
+      const testRunId = generateTestRunId(testInfo.workerIndex);
+      const appUrl = baseURL || 'http://localhost:4242';
+      let client: SimulatedE2EClient | null = null;
+
+      try {
+        // 1. Create user and set up client
+        const user = await createTestUser(testRunId);
+        const syncConfig = getSuperSyncConfig(user);
+        console.log(`[Account-Deletion] Created user ${user.userId}`);
+
+        client = await createSimulatedClient(browser, appUrl, 'A', testRunId);
+        await client.sync.setupSuperSync(syncConfig);
+
+        // Create a task and sync to verify everything works
+        const taskName = `Pre-Delete-Task-${testRunId}`;
+        await client.workView.addTask(taskName);
+        await client.sync.syncAndWait();
+        await waitForTask(client.page, taskName);
+        console.log('[Account-Deletion] ✓ Initial sync successful');
+
+        // 2. Delete the user account on the server
+        await deleteTestUser(user.userId);
+        console.log(`[Account-Deletion] ✓ Deleted user ${user.userId}`);
+
+        // 3. Try to sync again - should fail with auth error
+        await client.sync.triggerSync();
+
+        // 4. Wait for error indicator to appear
+        // The sync button should show error state (sync_problem icon),
+        // or a snackbar with error message should appear
+        const errorIndicator = client.page.locator(
+          // Error snackbar with any of these indicators
+          'simple-snack-bar:has-text("Configure"), ' +
+            'simple-snack-bar:has-text("error"), ' +
+            'simple-snack-bar:has-text("401"), ' +
+            'simple-snack-bar:has-text("403"), ' +
+            'simple-snack-bar:has-text("Authentication"), ' +
+            // Or sync button showing error icon
+            '.sync-btn mat-icon:has-text("sync_problem")',
+        );
+
+        await expect(errorIndicator.first()).toBeVisible({ timeout: 20000 });
+        console.log('[Account-Deletion] ✓ Client detected auth failure');
+      } finally {
+        if (client) await closeClient(client);
+      }
+    },
+  );
+
+  /**
+   * Scenario: Client can reconfigure after account deletion and re-registration
+   *
+   * Tests that after account deletion, a client can be reconfigured
+   * with new credentials and resume syncing.
+   *
+   * Actions:
+   * 1. Create user A, set up client, sync successfully
+   * 2. Delete user A account
+   * 3. Create user B (new account)
+   * 4. Reconfigure client with user B credentials
+   * 5. Verify sync works with new account
+   */
+  base(
+    'Client can reconfigure with new account after deletion',
+    async ({ browser, baseURL }, testInfo) => {
+      testInfo.setTimeout(120000);
+      const testRunId = generateTestRunId(testInfo.workerIndex);
+      const appUrl = baseURL || 'http://localhost:4242';
+      let client: SimulatedE2EClient | null = null;
+
+      try {
+        // 1. Create first user and sync
+        const userA = await createTestUser(`${testRunId}-A`);
+        const configA = getSuperSyncConfig(userA);
+        console.log(`[Reconfigure] Created user A: ${userA.userId}`);
+
+        client = await createSimulatedClient(browser, appUrl, 'Client', testRunId);
+        await client.sync.setupSuperSync(configA);
+
+        const task1 = `UserA-Task-${testRunId}`;
+        await client.workView.addTask(task1);
+        await client.sync.syncAndWait();
+        console.log('[Reconfigure] ✓ User A sync successful');
+
+        // 2. Delete user A account
+        await deleteTestUser(userA.userId);
+        console.log('[Reconfigure] ✓ Deleted user A');
+
+        // 3. Create user B (new account)
+        const userB = await createTestUser(`${testRunId}-B`);
+        const configB = getSuperSyncConfig(userB);
+        console.log(`[Reconfigure] ✓ Created user B: ${userB.userId}`);
+
+        // 4. Reconfigure client with user B credentials
+        // Open sync settings via right-click
+        await client.sync.syncBtn.click({ button: 'right' });
+        await client.sync.providerSelect.waitFor({ state: 'visible', timeout: 10000 });
+
+        // Update access token
+        await client.sync.accessTokenInput.clear();
+        await client.sync.accessTokenInput.fill(configB.accessToken);
+
+        // Save configuration
+        await client.sync.saveBtn.click();
+        await client.page
+          .locator('mat-dialog-container')
+          .waitFor({ state: 'detached', timeout: 5000 })
+          .catch(() => {});
+
+        // Wait for any dialogs to settle
+        await client.page.waitForTimeout(1000);
+
+        // 5. Sync and verify it works with user B
+        await client.sync.syncAndWait();
+
+        // Create a new task with user B
+        const task2 = `UserB-Task-${testRunId}`;
+        await client.workView.addTask(task2);
+        await client.sync.syncAndWait();
+
+        // Verify task exists
+        await waitForTask(client.page, task2);
+        console.log('[Reconfigure] ✓ User B sync successful - reconfiguration complete');
+      } finally {
+        if (client) await closeClient(client);
+      }
+    },
+  );
+});
diff --git a/e2e/utils/supersync-helpers.ts b/e2e/utils/supersync-helpers.ts
index cc009321f6..0b3f1e91c4 100644
--- a/e2e/utils/supersync-helpers.ts
+++ b/e2e/utils/supersync-helpers.ts
@@ -94,6 +94,23 @@ export const cleanupTestData = async (): Promise<void> => {
   }
 };
 
+/**
+ * Delete a specific test user account on the SuperSync server.
+ * Used to test account deletion and re-registration scenarios.
+ *
+ * @param userId - The user ID to delete
+ */
+export const deleteTestUser = async (userId: number): Promise<void> => {
+  const response = await fetch(`${SUPERSYNC_BASE_URL}/api/test/user/${userId}`, {
+    method: 'DELETE',
+  });
+
+  if (!response.ok && response.status !== 404) {
+    const text = await response.text();
+    throw new Error(`Failed to delete test user: ${response.status} - ${text}`);
+  }
+};
+
 /**
  * Check if the SuperSync server is running, healthy, AND has test mode enabled.
  * Tests require TEST_MODE=true on the server for the /api/test/* endpoints.
diff --git a/packages/super-sync-server/src/test-routes.ts b/packages/super-sync-server/src/test-routes.ts
index 9e1394d090..3eeff098f1 100644
--- a/packages/super-sync-server/src/test-routes.ts
+++ b/packages/super-sync-server/src/test-routes.ts
@@ -149,5 +149,47 @@ export const testRoutes = async (fastify: FastifyInstance): Promise<void> => {
     },
   );
 
+  /**
+   * Delete a test user by userId.
+   * Used by E2E tests to simulate account deletion scenarios.
+   */
+  fastify.delete<{ Params: { userId: string } }>(
+    '/user/:userId',
+    {
+      schema: {
+        params: {
+          type: 'object',
+          required: ['userId'],
+          properties: {
+            userId: { type: 'string' },
+          },
+        },
+      },
+      config: {
+        rateLimit: false,
+      },
+    },
+    async (request, reply) => {
+      const userId = parseInt(request.params.userId, 10);
+
+      if (isNaN(userId)) {
+        return reply.status(400).send({ error: 'Invalid userId' });
+      }
+
+      try {
+        // CASCADE delete handles: operations, syncState, devices (via Prisma schema)
+        await prisma.user.delete({ where: { id: userId } });
+        Logger.info(`[TEST] Deleted test user ID: ${userId}`);
+        return reply.send({ deleted: true, userId });
+      } catch (err: unknown) {
+        Logger.error('[TEST] Failed to delete test user:', err);
+        return reply.status(404).send({
+          error: 'User not found or already deleted',
+          message: (err as Error).message,
+        });
+      }
+    },
+  );
+
   Logger.info('[TEST] Test routes registered at /api/test/*');
 };
diff --git a/src/app/pfapi/api/sync/providers/super-sync/super-sync.spec.ts b/src/app/pfapi/api/sync/providers/super-sync/super-sync.spec.ts
index 533ed52709..1d192b0583 100644
--- a/src/app/pfapi/api/sync/providers/super-sync/super-sync.spec.ts
+++ b/src/app/pfapi/api/sync/providers/super-sync/super-sync.spec.ts
@@ -2,7 +2,7 @@ import { SuperSyncProvider } from './super-sync';
 import { SuperSyncPrivateCfg } from './super-sync.model';
 import { SyncProviderPrivateCfgStore } from '../../sync-provider-private-cfg-store';
 import { SyncProviderId } from '../../../pfapi.const';
-import { MissingCredentialsSPError } from '../../../errors/errors';
+import { MissingCredentialsSPError, AuthFailSPError } from '../../../errors/errors';
 import { SyncOperation } from '../../sync-provider.interface';
 
 // Helper to decompress gzip Uint8Array to string
@@ -479,20 +479,20 @@ describe('SuperSyncProvider', () => {
   });
 
   describe('error handling', () => {
-    it('should include error text in API error message', async () => {
+    it('should include error text in API error message for non-auth errors', async () => {
       mockPrivateCfgStore.load.and.returnValue(Promise.resolve(testConfig));
 
       fetchSpy.and.returnValue(
         Promise.resolve({
           ok: false,
-          status: 401,
-          statusText: 'Unauthorized',
-          text: () => Promise.resolve('Invalid token'),
+          status: 500,
+          statusText: 'Internal Server Error',
+          text: () => Promise.resolve('Database connection failed'),
         } as Response),
       );
 
       await expectAsync(provider.downloadOps(0)).toBeRejectedWithError(
-        'SuperSync API error: 401 Unauthorized - Invalid token',
+        'SuperSync API error: 500 Internal Server Error - Database connection failed',
       );
     });
 
@@ -552,6 +552,137 @@ describe('SuperSyncProvider', () => {
     });
   });
 
+  describe('authentication error handling', () => {
+    it('should throw AuthFailSPError on 401 Unauthorized response', async () => {
+      mockPrivateCfgStore.load.and.returnValue(Promise.resolve(testConfig));
+
+      fetchSpy.and.returnValue(
+        Promise.resolve({
+          ok: false,
+          status: 401,
+          statusText: 'Unauthorized',
+          text: () => Promise.resolve('Invalid or expired token'),
+        } as Response),
+      );
+
+      await expectAsync(provider.downloadOps(0)).toBeRejectedWith(
+        jasmine.any(AuthFailSPError),
+      );
+    });
+
+    it('should throw AuthFailSPError on 403 Forbidden response', async () => {
+      mockPrivateCfgStore.load.and.returnValue(Promise.resolve(testConfig));
+
+      fetchSpy.and.returnValue(
+        Promise.resolve({
+          ok: false,
+          status: 403,
+          statusText: 'Forbidden',
+          text: () => Promise.resolve('Account deleted'),
+        } as Response),
+      );
+
+      await expectAsync(provider.downloadOps(0)).toBeRejectedWith(
+        jasmine.any(AuthFailSPError),
+      );
+    });
+
+    it('should clear cached config on auth failure', async () => {
+      // First call succeeds - config gets cached
+      mockPrivateCfgStore.load.and.returnValue(Promise.resolve(testConfig));
+      fetchSpy.and.returnValue(
+        Promise.resolve({
+          ok: true,
+          json: () => Promise.resolve({ ops: [], hasMore: false, latestSeq: 0 }),
+        } as Response),
+      );
+      await provider.downloadOps(0);
+      expect(mockPrivateCfgStore.load).toHaveBeenCalledTimes(1);
+
+      // Second call fails with 401
+      fetchSpy.and.returnValue(
+        Promise.resolve({
+          ok: false,
+          status: 401,
+          statusText: 'Unauthorized',
+          text: () => Promise.resolve('Token expired'),
+        } as Response),
+      );
+
+      try {
+        await provider.downloadOps(0);
+      } catch (e) {
+        // Expected to throw AuthFailSPError
+        expect(e).toBeInstanceOf(AuthFailSPError);
+      }
+
+      // Third call should reload config from store (cache was cleared)
+      fetchSpy.and.returnValue(
+        Promise.resolve({
+          ok: true,
+          json: () => Promise.resolve({ ops: [], hasMore: false, latestSeq: 0 }),
+        } as Response),
+      );
+      await provider.downloadOps(0);
+      expect(mockPrivateCfgStore.load).toHaveBeenCalledTimes(2);
+    });
+
+    it('should throw AuthFailSPError for uploadOps on 401', async () => {
+      mockPrivateCfgStore.load.and.returnValue(Promise.resolve(testConfig));
+
+      fetchSpy.and.returnValue(
+        Promise.resolve({
+          ok: false,
+          status: 401,
+          statusText: 'Unauthorized',
+          text: () => Promise.resolve('Account not found'),
+        } as Response),
+      );
+
+      await expectAsync(
+        provider.uploadOps([createMockOperation()], 'client-1'),
+      ).toBeRejectedWith(jasmine.any(AuthFailSPError));
+    });
+
+    it('should throw AuthFailSPError for uploadSnapshot on 401', async () => {
+      mockPrivateCfgStore.load.and.returnValue(Promise.resolve(testConfig));
+
+      fetchSpy.and.returnValue(
+        Promise.resolve({
+          ok: false,
+          status: 401,
+          statusText: 'Unauthorized',
+          text: () => Promise.resolve('Invalid token'),
+        } as Response),
+      );
+
+      await expectAsync(
+        provider.uploadSnapshot({}, 'client-1', 'recovery', {}, 1),
+      ).toBeRejectedWith(jasmine.any(AuthFailSPError));
+    });
+
+    it('should include HTTP status code in AuthFailSPError message', async () => {
+      mockPrivateCfgStore.load.and.returnValue(Promise.resolve(testConfig));
+
+      fetchSpy.and.returnValue(
+        Promise.resolve({
+          ok: false,
+          status: 403,
+          statusText: 'Forbidden',
+          text: () => Promise.resolve('Access denied'),
+        } as Response),
+      );
+
+      try {
+        await provider.downloadOps(0);
+        fail('Expected AuthFailSPError to be thrown');
+      } catch (e) {
+        expect(e).toBeInstanceOf(AuthFailSPError);
+        expect((e as AuthFailSPError).message).toContain('403');
+      }
+    });
+  });
+
   describe('upload response with rejected ops', () => {
     it('should return response with CONFLICT_CONCURRENT rejection', async () => {
       mockPrivateCfgStore.load.and.returnValue(Promise.resolve(testConfig));
diff --git a/src/app/pfapi/api/sync/providers/super-sync/super-sync.ts b/src/app/pfapi/api/sync/providers/super-sync/super-sync.ts
index ddb2f246d3..47cf7db5a4 100644
--- a/src/app/pfapi/api/sync/providers/super-sync/super-sync.ts
+++ b/src/app/pfapi/api/sync/providers/super-sync/super-sync.ts
@@ -16,7 +16,7 @@ import {
 } from '../../sync-provider.interface';
 import { SyncProviderPrivateCfgStore } from '../../sync-provider-private-cfg-store';
 import { SuperSyncPrivateCfg } from './super-sync.model';
-import { MissingCredentialsSPError } from '../../../errors/errors';
+import { MissingCredentialsSPError, AuthFailSPError } from '../../../errors/errors';
 import { SyncLog } from '../../../../../core/log';
 import {
   compressWithGzip,
@@ -347,6 +347,20 @@ export class SuperSyncProvider
     return this._cachedServerSeqKey;
   }
 
+  /**
+   * Check HTTP response status and throw AuthFailSPError for auth failures.
+   * Clears cached config so next operation will reload from store.
+   */
+  private _checkHttpStatus(status: number, body?: string): void {
+    if (status === 401 || status === 403) {
+      // Clear cached config so next operation will reload from store
+      // (allowing user to re-configure after auth failure)
+      this._cachedCfg = undefined;
+      this._cachedServerSeqKey = undefined;
+      throw new AuthFailSPError(`Authentication failed (HTTP ${status})`, body);
+    }
+  }
+
   private async _fetchApi<T>(
     cfg: SuperSyncPrivateCfg,
     path: string,
@@ -370,6 +384,8 @@ export class SuperSyncProvider
 
     if (!response.ok) {
       const errorText = await response.text().catch(() => 'Unknown error');
+      // Check for auth failure FIRST before throwing generic error
+      this._checkHttpStatus(response.status, errorText);
       throw new Error(
         `SuperSync API error: ${response.status} ${response.statusText} - ${errorText}`,
       );
@@ -407,6 +423,8 @@ export class SuperSyncProvider
 
     if (!response.ok) {
       const errorText = await response.text().catch(() => 'Unknown error');
+      // Check for auth failure FIRST before throwing generic error
+      this._checkHttpStatus(response.status, errorText);
       throw new Error(
         `SuperSync API error: ${response.status} ${response.statusText} - ${errorText}`,
       );
@@ -457,6 +475,8 @@ export class SuperSyncProvider
     if (response.status < 200 || response.status >= 300) {
       const errorData =
         typeof response.data === 'string' ? response.data : JSON.stringify(response.data);
+      // Check for auth failure FIRST before throwing generic error
+      this._checkHttpStatus(response.status, errorData);
       throw new Error(`SuperSync API error: ${response.status} - ${errorData}`);
     }